1. Field of the Invention
The present invention relates to revolving security doors and so-called, man-traps.
2. Description of Related Art
Security doors and, so-called man-traps (hereinafter individually and collectively referred to as “security doors” or “security door”) are used in airports, banks, commercial buildings, military installations, and other locations where restricted access is desirable. In many instances, such security doors are embodied as revolving doors. In a common, non-limiting, embodiment of a revolving security door, a person inserts a pass card into a card reader that is interfaced with a control system for the door, and enters a chamber on one side of the door. If the card is authorized, the door will turn its panels or wings and thus each chamber until the entered chamber moves from a first door opening, e.g., the entrance, to a second door opening, e.g., the exit. As the entered chamber passes from the first door opening to the second door opening, all of the other chambers move by a corresponding amount. Therefore, it is possible for an unauthorized person to “tailgate”, i.e., to enter a chamber located at the second door opening or a door opening immediately following the enclosed chamber, or to “piggyback”, i.e., to enter the same compartment as the authorized person. In such situations, prior art systems stop the door thereby trapping the unauthorized person in a chamber. If the door has a “trapped man” feature to detect such a situation, the control system will cause the door to reversely rotate after stopping to force the unauthorized “trapped” person back to his starting point. If the door is not equipped with such a “trapped man” feature, the next authorized party to enter the doorway will allow the unauthorized party to pass to the exit. In the situation where a “tailgater” is attempting to pass from the second door opening to the first door opening, the system may also detect him and return him to his starting point before allowing his compartment to reach the entrance.
One way that tailgating has been detected is by the use of floor mats in the security door to detect when a compartment has been entered. However, such mats have several drawbacks. First, rain, snow, dirt or other foreign matter can often cause mat failures. Second, a mat cannot detect a person or object such as a gun or a security pass card attached to the door frame. Third, it is difficult to make a mat sufficiently sensitive to lightweight objects. Fourth, the construction of certain revolving security doors makes it possible for a person to not touch a floor mat in the security door as the door passes between a first door opening and a second door opening thereof. Such construction can include a ledge adjacent the base of one or more door wings where a person can stand above the floor mat during rotation of the revolving door. Moreover, it is envisioned that an unauthorized object, such as a weapon, could be secured, e.g., taped, to the surface of a door wing whereupon said object could pass the openings of the revolving door without contacting the floor mat thereof. Accordingly, there is a need to more accurately and reliably detect whether unauthorized persons or objects have entered a compartment of a revolving security door.
It has been proposed to use ultrasonic sensors instead of mats, but use of such sensors in a revolving door presents problems. First, it is well known that the low frequencies used by ultrasound sensors are near the upper frequency hearing limit of human beings and, therefore, the output of ultrasound sensors may be detectable by certain individuals having an extended frequency hearing. Second, it is well known that ultrasound waves used by ultrasound sensors are susceptible to distortion by moving air which can be caused either by rotation of the door in use or by a flow of air through the door caused by the difference in positive air pressure inside a building in which the door is installed due to the operation of the buildings' HVAC system and a lower air pressure outside the building. Such movement of air can distort the ultrasound waves rendering detection of objects or persons difficult. Third, to detect small objects such as pass cards or firearms, the sensors must have a high gain. Such high gain increases the likelihood that reverberations or echoes will cause false readings. This is especially true in a security revolving door which has a substantially closed housing. Similarly, the greater the range (portion of the floor to ceiling distance) covered by the sensor, the greater the likelihood of false readings due primarily to echoes from the floor. Furthermore, such sensors do not have the ability to distinguish between an actual object or person located in one of the compartments and on one of the door wings.
Accordingly, a need exists for a control system for a revolving security door with the ability to positively identify a person or object passing from one side of the revolving door to the other while ignoring the door wings.